Electron beam furnaces and coaters are used to heat materials to produce vapors for deposition on an article. An electron beam furnace includes an electron gun, a deflection system, and a cooling system. The electron gun generates an electron beam. The deflection system directs the electron beam toward the material to be heated. The cooling system cools the electron gun to prevent it from overheating.
An electron gun typically includes an electron source, a focusing electrode, and an accelerating electrode. The electron source is typically a cathode heated by an electric current to cause the cathode to emit electrons. The focusing electrode is typically negatively charged to repel the electrons and thereby direct the electrons in a direction generally toward the accelerating electrode. The accelerating electrode is typically less negatively charged than the electron source and the focusing electrode to cause the electrons to form into a beam and travel in the downstream direction.
In one known type of electron gun, the electron source and the focusing electrode are elongated and disposed in a head. The head is supported by a platform spaced apart from the accelerating electrode. This type of electron gun is reliable and available in many different power ratings. The physical size of the head, the accelerating electrode, and the platform of a given one of these electron guns depends on its power rating.
During operation the electron beam generates ions, the ions move in the reverse direction relative to the motion of the electrons and accelerate in the electric field between the cathode and anode. As these high energy ions strike the cathode surface, the ions cause the cathode material to diffuse and vaporize. The cathode eventually deforms due to constant reflected electron bombardment and erodes away. Cathode deformation also impacts the performance of the electron gun. The evaporation rate of the electron gun becomes altered. As a result, the average life and overall useful life of the electron gun becomes significantly reduced. In turn, one's ability to coat a requisite number of targets in assembly is hampered and overall productivity is significantly affected.
Consequently, there exists a need for an electron gun assembly constructed to increase service and active life of the electron gun as well as permit the quick and efficient replacement of the thermion source without restricting the power rating of the electron gun.